Nitrilotriacetonitrile (NTAN) is a well known intermediate in the preparation of nitrilotriacetic acid (NTA) and salts thereof, which are useful as sequestering agents in detergents, etc. Typical processes for producing NTAN are disclosed in U.S. Pat. No. 3,504,011, U.S. Pat. No. 3,515,742 and U.S. Pat. No. 3,061,628.
Nitriles can polymerize, depending upon the pH. They can also spontaneously eliminate HCN, or there can be residual cyanide present in the nitrile from its preparation. Indeed, one of the methods of NTAN preparation is in accordance with the following general equation, wherein HCN is a reactant: EQU NH.sub.3 +3HCHO+3HCN.fwdarw.N(CH.sub.2 CN).sub.3
Similarly, HCN can itself polymerize, as can the nitrile residue of the HCN elimination. These phenomena are accelerated by heat, depending on the structure of the nitrile.
A particular problem is presented with solid nitriles when the same are heated in solution. Specifically, a slow degradation takes place, marked by gradually increasing discoloration of the solution, until the solution becomes dark brown or black with the eventual appearance of solids. Where such a solution is to be used as feedstock for a hydrogenation process to convert the nitrile to an amine or some intermediate, such as is disclosed in U.S. Pat. No. 5,097,072, the metal catalyst that is typically used in such a process quickly becomes inactive. It is believed that the catalyst is poisoned either by cyanide or by cyanide and nitrile polymers. Once so poisoned, the catalyst cannot be reactivated.
It is therefore an object of the present invention to provide a means for the stabilization of nitriles, and in particular, NTAN.
It is a further object to avoid rapid deactivation of catalyst by stabilizing nitrile reactants.